JP2000-142146A published by the Japanese Patent Office in 2000 discloses a drivetrain for a hybrid vehicle which is constructed by connecting a generator, an engine and a motor for driving a vehicle to a sun gear, a planetary carrier and a ring gear of a planetary gear mechanism. According to this drivetrain, the continuously variable speed change and the increase or decrease of the output torque can be performed by using the differential function of the gears to distribute the engine output partially to the generator and supplying the generated electric power to the motor.